1. Field of the Invention
This invention relates to a novel organic compound and a liquid crystal composition containing the same. More particularly it relates to an optically active compound having an optically active group, a liquid crystal composition containing the same, and an electrooptical device using the composition.
2. Description of the Related Art
Liquid crystal display devices having superior specific features such as low voltage operation, small power consumption, flat panel display, etc. have recently been broadly used for television, computer terminal, particularly display terminal of movable goods, not to mention watches, electronic calculator, instruments, etc. Most of these goods have been employing TN (twist nematic) display mode. Further, STN mode having improved TN mode by increasing the twist angle to 180.degree.-270.degree. has also been gradually employed. These display modes are inferior in the aspect of response time to emissive mode display devices such as cathode ray tube, electroluminescence, plasma display, etc. Thus, various efforts of improvement have been made, but a TN mode device of high speed response has not yet been realized. However, in the case of a novel display mode using ferroelectric liquid crystals, the research on which has recently been actively developed, the response time has been notably shortened (Clark et al, Applied Phys. lett., 36, 899 (1980)). This display mode is directed to a method utilizing chiral smectic phases such as chiral smectic C phase (hereinafter abbreviated to SC*), etc. exhibiting ferroelectricity. It has been known that phases exhibiting ferroelectricity are not only SC* phase, but also chiral smectic F, chiral smectic G, chiral smectic H, chiral smectic I, etc.
Practical ferroelectric liquid crystal materials are liquid crystal compositions obtained by mixing a plurality of liquid crystal compounds or non-liquid crystal compounds, and a further improvement in material characteristics thereof has been required.
Such liquid crystal materials are not only those composed only of ferroelectric liquid crystal compounds, but also the materials may be composed by adding at least one kind of optically active substances to compounds or compositions exhibiting achiral smectic C, F, G, H, I or the like phase (hereinafter abbreviated to SC or the like phase), as basic substances. However, such optically active substances are preferred to exhibit liquid crystal phases, preferably ferroelectric liquid crystal phases. Even in the case that the substances exhibit no liquid crystal phases, the substances are preferred to have a structure similar to those of liquid crystal compounds, that is, to be quasi liquid crystal substances.
The ferroelectric liquid crystal display mode makes it possible to realize a response speed hundreds of times to thousands of times as quick as that of TN mode, and to exhibit memory effect due to bistability; thus various use applications of the mode including television having a flat panel and large area, high speed light shutter, etc. have been expected.
The present inventors have disclosed the following compounds having two adjacent rings at the central part thereof: ##STR3## (Japanese patent application laid-open No. Hei 1-128598/ 1989). However, all of these compounds exhibit only melting points as phase transition points. Further, even in the case that these compounds are added to achiral smectic C liquid crystal compositions, the induced ferroelectric mesomorphic ranges are far inferior to those prior to the addition. Thus, improvement of the compounds has been desired.